io_uring: disallow modification of rsrc_data during quiesce

io_rsrc_ref_quiesce will unlock the uring while it waits for references to
the io_rsrc_data to be killed.
There are other places to the data that might add references to data via
calls to io_rsrc_node_switch.
There is a race condition where this reference can be added after the
completion has been signalled. At this point the io_rsrc_ref_quiesce call
will wake up and relock the uring, assuming the data is unused and can be
freed - although it is actually being used.

To fix this check in io_rsrc_ref_quiesce if a resource has been revived.

Reported-by: syzbot+ca8bf833622a1662745b@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220222161751.995746-1-dylany@fb.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -7926,8 +7926,16 @@ static __cold int io_rsrc_ref_quiesce(struct io_rsrc_data *data,
 		ret = wait_for_completion_interruptible(&data->done);
 		if (!ret) {
 			mutex_lock(&ctx->uring_lock);
+			if (atomic_read(&data->refs) > 0) {
+				/*
+				 * it has been revived by another thread while
+				 * we were unlocked
+				 */
+				mutex_unlock(&ctx->uring_lock);
+			} else {
 				break;
 			}
+		}
 
 		atomic_inc(&data->refs);
 		/* wait for all works potentially completing data->done */